Method for measuring position and angle

ABSTRACT

Method for position measurement, whereby a magnetic field is generated in a measuring volume comprising one or several elongated elements of amorphous material, the magnetic properties of which being influenced by the magnetic field, is arranged in the measuring volume. The measuring volume is composed of several sub-volumes, and the extension of the sub-volumes in the desired measuring direction is chosen in such a way that the extension corresponds to the desired measuring resolution in the measuring directions. The change in magnetic or mechanical properties of the element caused by the magnetic flux intensity in the respective sub-volume along the longitudinal direction of the element is detected, the change being a measure of the position of the element.

BACKGROUND OF THE INVENTION

Method and device for measuring position and angle with variableaccuracy.

When measuring the position a measuring body or an angular alignment ofthe measuring body in relation to a reference axis it is of advantage ifthe measuring body can move freely in a measuring volume, i.e. withoutbearing on a measuring path or the like. It would also be of advantageif the sensing of the measuring body could take place without contact.

SUMMARY OF THE INVENTION

One object of the present invention is to achieve a method and a devicewhich makes such a measurement possible. Furthermore, according to afurther development of the invention a procedure has been achieved whichmakes a dynamically adjustable accuracy of measurement possible in agiven measurement volume.

The measurement procedure according to the present invention is based oncertain magnetic and mechanical properties of element in the shape ofbands, threads or strips of a material which is amorphously changed whenthe elements are exposed to a magnetic field, what is called a biasfield. For example the position/direction of the element is related tothe magnetic field in the longitudinal or axial direction of theamorphous element, thereby making the mechanical resonance frequency ofthe element a measure of the position/direction of the element. The sameprocedure is adaptable for a measuring component comprising an amorphouselement which is magnetically connected to an inductive element which inturn is a part of an electric resonance circuit. When the magnetic fieldis changed, the magnetic properties of the amorphous elements arechanged so that the inductance of the inductive element is changed.Thereby the resonance frequency of the electric resonance circuit isalso changed.

Other materials than amorphous materials are also applicable accordingto the invention. The crucial property of the material is itscharacteristics, e.g. magnetic or elastic properties, are influenced bymagnetic fields. The influence should be of such an extent that thechange in properties can be measurable by remote detection. Examples arematerials which are magnetoresistive, the electric conductivity of whichare changed in dependence of the magnetic field, and magnetooptical, thelight conducting property of which are changed in dependence of appliedmagnetic field. For materials of the latter type that phenomonen whichis called the Faraday-effect can be used, i.e. the plane of oscillationfor polarized light is rotated, the deflection angle being proportionalto the magnetized field strength, or the phenomonen which is called theKerrer-effect, whereby a similar effect of certain materials is achievedby the influence of an electric field.

The resonance frequency of an amorphous element exhibiting acomparatively great magneto-mechanical coupling is varied with theintensity of the magnetic flow along the main direction of the elementby what is called the delta-E-effect. Thus, if this intensity ofmagnetic flow is changed as a function of the position/direction of theamorphous element the resonance frequency of the amorphous element willbe a function of its position/direction. It is very advantageous to givethe measuring information in form of a frequency value since such avalue is very immune to noise. Furthermore, mixed information fromseveral measurement transmitters operating on different frequency bandscan be transmitted together on one information channel.

In order to achieve an enhanced position of measurement procedures canbe used where several amorphous elements are placed in a measuring body.In these instances it is also suitable to register difference and sumfrequencies. By utilizing such differential measurement proceduressources of errors can be eliminated, such as for example distortion ofthe system caused by temperature, properties of the material, changes inthe field, etc.

It should be noted that the effective magnetic field along the axialdirection of the amorphous element is not necessarily equal to theprojection of the total field vector along the amorphous element. By theflux conductive property and geometry of the amorphous element thisrelationship can deviate from a pure projection. However, therelationship can always be mapped and thereby still permit a base forposition/angular measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described with reference to theembodiments shown in the accompanying drawings, wherein

FIG. 1 schematically shows field lines of a magnetic field whilepracticizing a measuring procedure according to the invention,

FIG. 2 schematically shows field lines of a magnetic field whilepracticizing an alternative measuring procedure according to theinvention,

FIG. 3 schematically shows field lines of a magnetic field whilepracticizing another alternative measuring procedure according to theinvention,

FIG. 4 schematically shows a practical embodiment of a measuring deviceaccording to the invention for measuring the position of a measuringbody,

FIG. 5 schematically shows an alternative practical embodiment of ameasuring device according to the invention for measuring the positionof a measuring body,

FIG. 6 schematically shows a practical embodiment of a measuring deviceaccording to the invention for measuring the angular alignment of ameasuring body,

FIG. 7 schematically shows an alternative practical embodiment of ameasuring device according to the invention for measuring the angularalignment of a measuring body,

FIGS. 8A and 8B schematically shows a further development of a measuringdevice according to the invention for measuring the position of ameasuring body and

FIG. 9 schematically shows an embodiment of the invention fordetermining the position and orientation of a measuring body in threedimensions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically shows the function when measuring the positionaccording to one embodiment of the invention. An element 10 of amorphousmaterial is placed with its longitudinal direction parallel to the fieldlines of a magnetic field Φ which is generated in a measuring volume.The increasing density of field lines in FIG. 1 indicates that a fieldgradient is present within the magnetic field. The field gradient isaligned perpendicular to the field direction. By placing the element 10within a measuring body which is movable in the direction of the thefield gradient the element 10 will be subjected to a magnetizing fieldstrength H of different magnitude in dependence of the position of theelement. As already has been described in the beginning of thedescription a change in strength of the magnetic field working in thelongitudinal direction of the element 10 results in a change in themagnetic properties of the element. These are detectable, either by thechange of the mechanical resonance frequency of the element and thus thechange of the magnetic field around the element or by the element beingcoupled to an inductive element which is a part of an electric resonancecircuit, the resonance frequency of which is changed when the magneticproperties of the element 10 is changed.

In the embodiment according to FIG. 2 a magnetic field has beengenerated with a field gradient directed leftwards in the figure. Thisis evident from the longer lines of force in the left part of thefigure. Here the element 10 is movable parallel to the field gradient inthe direction of the arrow A.

Another embodiment with a magnetic bias field is shown in FIG. 3. Inthis embodiment the magnetic field has a constant intensity along themeasuring distance but the field direction is changed, thus exposing theelement 10 in its longitudinal direction for magnetic fields ofdifferent magnitudes in dependence of its position. In this embodiment,according to FIG. 3, the element moves horizontally in the direction ofthe arrow A.

FIG. 4 shows in a simplified form how a magnetic field according to FIG.1 can be achieved. A magnet 11, which can be a permanent magnet or anelectromagnet, generates a magnetic field which is indicated by thecurved field lines from the north pole to the south pole of the magnet.If the magnetized field strength along the direction of a motion of theelement 10 is completely known the magnetic properties of the element 10are in every point along the direction of the motion directly related tothe position of the element. It is also possible by a calibrationprocedure to obtain an indication of the magnetic properties in everypoint, whereby this indication later on can be used reversely for thedetermination of the position of the element.

FIG. 5 shows a simplified embodiment for obtaining a measurementaccording to FIG. 4. A coil 12 with varying pitch ratio is arranged withits extension length in the direction of motion of the element 10. Theelement 10 is movable, either inside the coil or outside in a directionwhich is parallel to the center axis of the coil. As to the rest, themeasuring procedure according to FIG. 5 corresponds with the proceduredescribed in FIG. 4.

FIG. 6 shows schematically an embodiment for angular measurementaccording to the invention. A magnetic field Φ is generated by a magnet11 which can be a permanent magnet or an electromagnet. The field linesfrom the magnetic field are substantially parallel in one plane and theelement is arranged rotatable in this plane. The vital and detectablemagnetic properties of the element 10 is thereby directly related to theangular alignment of the element 10 in comparision with a referencedirection (REF). Measurements according to this embodiment results inangular alignments within the interval 0°-90°.

By arranging two elements 10 of different lengths fixed with a certainangular displacement in relation to each other measurements within theinterval 0°-180° are possible.

Nor is it necessary that the field lines are quite parallel. If thefield picture is known in that plane which the element, or elements, aremoving, or if the calibration procedure described above is used, angularmeasurements can nevertheless be performed.

Alternatively, the magnetic field can be rotated/thrown over betweendifferent known directions, thereby eliminating ambiguities indetection.

A further embodiment for angular measurement utilizes three orthogonal,known magnetic fields. Thereby it is possible to determine the directionof an amorphous element in three dimensions (azimuth and elevation).

It is also possible by a calibration procedure to determine therelationship between the orientation of the amorphous element and itsresonance frequency. If this is accomplished with an arbitrary magneticfield which varies with the rotation angle/angles a complete angulardetermination is possible.

A further alternative embodiment is as follows. When passing theresonance frequency of the amorphous element with an exciting signalfrequency a marked phase shift takes place between the excited anddetected (amorphous) signal.

An alternative procedure for measuring position/angle can thus be toexcite with a fixed frequency and instead measuring the phase levelbetween excitation and detection when the position of the amorphouselement is varied around that position/orientation in a chosen biaswhich gives a resonance that is equal to the chosen, fixed excitingfrequency. Again, a possibility can be seen for a high performancemeasurement around an arbitrary chosen (with the combination of biasedand fixed frequency) point along the measuring interval.

A further embodiment for angular measurement is evident from FIG. 7. Acoil 11 generates a magnetic field which is directed through two flowconduits formed as shanks 13, between which a magnetic field in that wayis directed. The shanks 13 are flat, substantially parallel plates whichare bent in one plane. The shanks are also somewhat tapered towardstheir free ends. An element 10 is pivotally arranged in the area of thecentral point of the radius after which the shanks are curved. Theelement 10 extends inbetween the shanks. The measuring coil 14 isarranged around the element 10 in that area of the element which ispositioned between the shanks 13. A second measuring coil 15, howeveranti-phase winded, is arranged in series with the coil 14, the measuringcoil being positioned outside the magnetic field between the shanks 13during the total rotating movement of the element 10. By this embodimentdifferent types of disturbances from external sources generating amagnetic field which otherwise would influence the angular measurementnegatively are eliminated.

In FIGS. 8A and 8B an embodiment of measurement according to theinvention is shown, according to which the measurement accuracy can beadjusted dynamically over a measuring area or a measuring volume. Anamorphous element has a maximal working area, within which its magneticproperties are changed in a known way in relation to the magnetizingfield strength H. As shown in FIGS. 8A and 8B applicable measuring areais thus limited by a maximum and a minimum value of the magnetizingfield strength H (H_(max) and H_(min), respectively). In a first stageof the measurement the distance between H_(max) and H_(min) is utilizedover the total measuring area, which is marked by the line I in FIGS. 8Aand 8B. As shown in FIG. 8B, the magnetizing field strength H can beachieved by leading an electric current with continuously increasingstrength into the coil system 15 which is arranged at the measuringdistance. In the embodiment shown in FIGS. 8A and 8B the current I₁ isgreater than the current I₉. When moving the element 10 in the directionof the arrow A, the position of the element is detected as a function ofthe actual magnetic properties of the element, for example its resonancefrequency. In order to increase the accuracy of measurement in a shorterinterval of the measuring distance, the current is increased throughsome of the coils present in the coil system 15 so as to attain amagnetizing field strength H according to the curve II. The totalworking area of the element 10 will then lie within a very narrowinterval of length and a very accurate measurement of the position isthus possible. The magnetizing field strength H with its desireddistribution can also be achieved in other ways. Several coils arrangedtogether in different geometries can for example be made to generate thefield strength by driving currents of different magnitudes through thedifferent coils.

In most cases the embodiments described above refer to a one- ortwo-dimensional measurement, but it is also quite possible to achievethe measurement in three dimensions by combining several coil systems.If a measuring object is provided with two elements of differentmagnetic properties, e.g. of different length, the elements being soarranged that they are angularly displaced from each other or parallellydisplaced in their transverse direction, the position of the object aswell as its orientation can be determined. This is evident from FIG. 9which shows three orthogonally arranged coil systems. A measuring body16 is arranged in that volume which on three sides is delimited by acoil system. Two elements 10 and 10' are arranged on the measuring body,the elements being rotated with a certain angle in relation to eachother. Each coil system comprises a coil 17 for generating a magneticbias field, a coil 18 for generating an exciting signal, and a coil 19for detection of the signal from the elements 10, 10'. In an alternativeembodiment, according to which the amorphous element is a part of anelectric resonance circuit, the coil 19 is replaced by an antenna.

One alternative procedure for increasing the resolution within a smallinterval of length is based on the resonance frequency of an element 10undergoing a drastic phase shift in relation to an exciting signal. Inthis procedure the signal in form of a sweep frequency is generated toexcite the element 10. When the sweep frequency passes the resonancefrequency of the element the latter is brought into self-oscillation.This corresponds to the normal measuring procedure. Then the excitingsignal is locked at the resonance frequency and the phase differencebetween exciting signal the respond signal generated from the element isdetected instead. Since the phase difference varies very strongly aroundthe point of resonance the resolution of detection thus becomes veryhigh.

An amorphous band can be brought to self-oscillation by a magnetic fieldof a certain signal form and/or frequence being generated in an excitingcoil. The signal form is suitably a short pulse but signals of morelasting nature can also be used. The exciting coil can be arranged atsome distance from the band and have a working area which covers thetotal measuring volume. It is also possible to arrange the exciting coildirectly adjacent to the band and in such a way that the exciting coilaccompanies the movement of the band in the measuring volume.

In order to detect and register the changed properties of an amorphousband in dependence of an external magnetic bias field, what is called abias-field, e.g. the resonance frequency of the band, it is suitable toarrange a detection coil or a pickup-coil. As for the exciting coil thedetection coil can be arranged at a distance from the band and have aworking area which covers the total measuring volume. It is alsopossible to directly arrange the detection coil adjacent to the band andin such a way that the exciting coil accompanies the movement of theband in the measuring volume. Of course, combinations of the coilembodiments mentioned above are also possible.

Since the measuring procedure according to the invention is based on theposition of an amorphous element in relation to an external magneticfield it is also possible to have the element fixedly arranged and themagnetic field being movable, rotatable or displaceable.

We claim:
 1. Method for position measurement, whereby a magnetic fieldhaving a flux intensity is generated in a measuring volume comprising atleast one elongated element of amorphous material, themagnetic/mechanical properties of which are influenced by the magneticfield, which is arranged in the measuring volume,providing the magneticfield with a gradient in the measuring volume; providing the measuringvolume with a plurality of sub-volumes; choosing extension of thesub-volumes in desired measuring directions in such a way that theextension corresponds to a desired measuring resolution in the measuringdirections; detecting a change in the magnetic/mechanical properties ofthe element caused by the magnetic flux intensity in a respectivesub-volume along a longitudinal direction of the element, the changebeing a measure of a position of the element; and the positionmeasurement comprising the steps of: measuring a gradient adapted to atotal length of a total measuring area and magnetic working area of theelement; and measuring a gradient adapted to a sub-distance of a lengthof the total measuring area of the element.
 2. Method as in claim 1,further comprising a step of providing the magnetic field with a knownstrength and direction in the longitudinal direction of the element ineach sub-volume.
 3. Method as in claim 1, further comprising a step ofbringing a plurality of elements of said at least one element toself-oscillation mechanically; anddetecting a resonance frequency of theplurality of elements as a position-determined measuring signal. 4.Method as in claim 1, further comprising a step of connecting theelement magnetically to an inductive element in an electric resonancecircuit.
 5. Method as in claim 1, further comprising a step of bringingthe gradient to adopt a known value in the measuring directions. 6.Method as in claim 5, further comprising a step of bringing the magneticfield to adopt a greater steepness concerning gradient in chosen regionsof the measuring volume.
 7. Method as in claim 1, further comprising thesteps of: generating the magnetic field in a uniform field direction inthe measuring volume and with the field gradient perpendicular to fielddirection; andproviding the amorphous element with its longitudinaldirection parallel to the field direction of the magnetic field, themeasuring direction being parallel to the field gradient.
 8. Method asin claim 1, further comprising the steps of: generating the magneticfield with a uniform field direction and with a field gradient parallelto the field direction; andarranging the amorphous element with itslongitudinal direction parallel to the field direction of the magneticfield, the measuring direction being parallel to the field gradient. 9.Method as in claim 3, further comprising the steps of: bringing theamorphous element to self-oscillation by an exciting signal of variablefrequency, a certain phase shift arising between the exciting signal anda signal transmitted by the amorphous element;locking the excitingsignal at the resonance frequency; and detecting a phase shift betweenthe exciting signal and the signal transmitted by the amorphous elementas a signal dependent on the position of the amorphous element.